The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium having not only an excellent durability and a good electromagnetic performance, but also a low light transmittance, a small surface resistivity and an excellent surface smoothness, and a filler contained in a magnetic recording layer constituting the magnetic recording medium.
With recent tendencies of miniaturization and weight reduction of video or audio magnetic recording and reproducing apparatuses as well as long-time recording by these apparatuses, magnetic recording media such as magnetic tapes or magnetic discs have been strongly required to have a high performance, namely high recording density, high durability, good electromagnetic performance or the like.
The magnetic recording media such as magnetic tapes or magnetic discs are contacted with a magnetic head upon recording and reproduction, so that a magnetic recording layer thereof tends to be abraded, resulting in contamination of the magnetic head as well as deterioration in recording and reproducing characteristics thereof. For this reason, it has been conventionally demanded to provide high-durability magnetic recording media having a high abrasion resistance.
Hitherto, in order to enhance an abrasion resistance of the magnetic recording layer of magnetic recording media, it has been attempted to incorporate various fillers such as alumina (Al2O3), hematite (xcex1-Fe2O3) and dichromium trioxide (Cr2O3) into the magnetic recording layer.
For instance, as magnetic recording media using alumina (Al2O3), there have been proposed magnetic recording media in which xcex1-Al2O3 particles containing an amorphous phase are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 5-36059(1993)), magnetic recording media in which xcex1-Al2O3 particles having a specific crystal structure are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 7-244836(1995)) and the like; as magnetic recording media using hematite (xcex1-Fe2O3), there have been proposed magnetic recording media in which granular xcex1-Fe2O3 particles are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 61-194628(1986)), magnetic recording media in which liquid hydrocarbon and xcex1-Fe2O3 particles are used (Japanese Patent Application Laid-Open (KOKAI) No. 54-70806(1979)) and the like; and as magnetic recording media using dichromium trioxide (Cr2O3), there have been proposed magnetic recording media in which acicular Cr2O3 particles are used as a filler (Japanese Patent Application Laid-Open (KOKAI) No. 62-112221(1987)) and the like.
Specifically, the magnetic recording medium described in Japanese Patent Application Laid-Open (KOKAI) No. 61-194628(1986) contains magnetic particles having a specific surface area of not less than about 28 m2/g and granular xcex1-Fe2O3 having an average particle diameter of about 0.05 to 1 xcexcm. This magnetic recording medium is produced by dispersing a mixture composed of 300 parts by weight of Co-coated xcex3-Fe2O3, 38 parts by weight of vinyl chloride-vinyl acetate copolymer, 24 parts by weight of polyurethane resin, 7 parts by weight of stearic acid, one part by weight of silicone oil, a prescribed amount of granular xcex1-Fe2O3 having a predetermined particle size and 800 parts by weight of a mixed solvent containing methyl ethyl ketone and toluene in equal amounts, for 40 minutes using a ball mill to prepare a magnetic coating composition, and then coating a base film with the magnetic coating composition.
However, these fillers have respective inherent problems. Namely, it is known that alumina shows a poor dispersibility in binder resin. With increase in amount of alumina added, the obtained magnetic recording medium is considerably deteriorated in electromagnetic performance. Hematite particles exhibit a relatively good dispersibility in binder resin. However, in order to obtain magnetic recording media having a sufficient durability, it is required to add a considerably large amount of the hematite particles thereto, resulting in deteriorated filling percentage of magnetic particles and, therefore, poor electromagnetic performance. Further, the use of dichromium trioxide is unfavorable from environmental and hygienic viewpoints.
It is also known that when the amount of these fillers added to the magnetic layer is increased, resultant magnetic recording media are improved in durability, but deteriorated in dispersibility of magnetic particles in vehicle, thereby causing a considerable deterioration in electromagnetic performance thereof.
Accordingly, it has been strongly demanded to provide magnetic recording media containing such a filler which does not adversely affect the dispersibility of magnetic particles in vehicle even when the filler is added in an amount sufficient to impart a high durability thereto, thereby preventing the magnetic recording media from being deteriorated in electromagnetic performance thereof.
In current general-purpose video tape systems, the end position of such a magnetic tape is recognized by detecting a transparent leader tape provided at the tape end thereof using a sensor. However, with recent demands for high-density recording on magnetic recording media, the particle size of magnetic particles used therein becomes much finer, so that a magnetic recording layer containing such magnetic particles has a high light transmittance. As a result, there arises the risk of occurrence of errors upon detecting the end position of the magnetic tape. Therefore, it has been strongly required that a magnetic recording portion of the magnetic tape has a sufficiently high blackness, i.e., a low light transmittance.
Further, it has been endlessly demanded to further improve characteristics of magnetic recording media. Therefore, it is strongly required to provide magnetic recording media having not only the above-described characteristics but also a small surface resistivity, an improved running property and the like.
The reasons therefor are as follows. When the surface resistivity of magnetic recording media is large, the amount of electrostatic charge thereon is increased, so that cut chips of the magnetic recording media or dusts are adhered onto the surfaces of the magnetic recording media upon production and use thereof, thereby causing problems such as increase in drop-outs.
It is widely known that carbon black fine particles as a black filler are incorporated into a magnetic recording layer. Also, there have been proposed magnetic recording media in which black titanium (TiO) particles are used as a black filler (Japanese Patent Publication (KOKOKU) Nos. 62-21185(1987) and 62-22179(1987)), magnetic recording media in which graphite fluoride is used a black filler (Japanese Patent Application Laid-Open (KOKAI) No. 56-156930(1981)), or the like.
Also, hitherto, with the reduction in thicknesses of magnetic recording layer and non-magnetic base film of magnetic recording media, it has been variously attempted to impart good surface smoothness and large stiffness thereto by improving a substrate on which the magnetic recording layer is formed. For instance, there has been proposed a non-magnetic substrate composed of a non-magnetic base film and at least one undercoat layer formed on the non-magnetic base film. The undercoat layer is composed of a binder and non-magnetic particles dispersed in the binder, which contain iron as a main component, e.g., acicular hematite particles or acicular iron oxide hydroxide particles (hereinafter referred to merely as xe2x80x9cnon-magnetic undercoat layerxe2x80x9d). Such a non-magnetic substrate is already put into practice (refer to Japanese Patent Publication (KOKOKU) No. 6-93297(1994), Japanese Patent Application Laid-Open (KOKAI) Nos. 62-159338(1987), 63-187418(1988), 4-167225(1992), 4-325915(1992), 5-73882(1993), 5-182177(1993), 5-347017(1993) and 6-60362(1994), or the like).
Thus, at present, it has been most strongly demanded to provide magnetic recording media having not only an excellent durability and a good electromagnetic performance, but also a low light transmittance, a small surface resistivity and a good surface smoothness. However, such magnetic recording media capable of satisfying all of these requirements have not been obtained yet.
The above-described conventional magnetic recording media containing a filler such as alumina, hematite or dichromium trioxide, are considerably deteriorated in electromagnetic performance when the amount of the filler added thereto is increased in order to enhance the durability thereof. Therefore, the use of these fillers has failed to produce magnetic recording media capable of exhibiting both excellent durability and good electromagnetic performance.
When carbon black fine particles are used as a black filler, it is possible to obtain magnetic recording media having a low light transmittance due to excellent blackness of the carbon black fine particles added. However, since the carbon black fine particles inherently show a poor dispersibility in vehicle, the dispersibility of magnetic particles in vehicle is also deteriorated, thereby adversely affecting properties of the obtained magnetic recording media, e.g., deterioration in electromagnetic performance, durability or the like. In this regard, Japanese Patent Application Laid-Open (KOKAI) No. 4-139619(1992) describes that xe2x80x9cWhen the binder resin and the magnetic particles are kneaded together to produce a coating material, if carbon black fine particles are added to the composition, there arises such a problem that the magnetic particles are deteriorated in orientation and filling property, as described below in Comparative Examples. Further, the carbon black particles are bulky particles having a bulk density of about 0.1 g/cm3, resulting in poor handling and processing properties thereof. Besides, the carbon black particles have problems concerning safety and hygiene such as carcinogenesisxe2x80x9d.
Thus, it has been demanded to provide a black filler as an alternate material of the carbon black fine particles. However, the above-described conventional fillers cannot contribute to sufficient reduction in light transmittance of magnetic recording media as compared to the carbon black fine particles, since alumina, hematite and dichromium trioxide show white, red and green colors, respectively.
Further, the black titanium tends to be readily oxidized and, therefore, is insufficient in stability in air. The graphite fluoride tends to suffer from the deterioration in electromagnetic performance due to poor dispersibility in binder resin.
As a result of the present inventors"" earnest studies for solving the above problems, it has been found that by using as a filler incorporated into a magnetic recording layer of a magnetic recording medium,
black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm and comprising:
hematite particles as core particles;
a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles,
the obtained magnetic recording medium is free from deterioration in electromagnetic performance even when the back filler is added thereto in an amount sufficient to enhance the durability thereof; and has an excellent durability and a good electromagnetic performance; and can be suitably used for high density recording because the black composite hematite particles which exhibit a sufficient blackness and are capable of considerably reducing the amount of carbon black used in combination therewith, are used as a black filler. The present invention has been attained on the basis of this finding.
It is an object of the present invention to provide a magnetic recording medium having not only an excellent durability and a good electromagnetic performance, but also a low light transmittance due to high blackness of a filler used therein and a small surface resistivity by using such a black filler capable of inhibiting the electromagnetic performance of the magnetic recording medium from being deteriorated even when the filler is added thereto in an amount sufficient in order to enhance the durability thereof.
It is another object of the present invention to provide a magnetic recording medium having not only an excellent durability and a good electromagnetic performance, but also a smooth surface, a lower light transmittance and a smaller surface resistivity, by using such a black filler capable of suppressing the deterioration of electromagnetic performance of the magnetic recording medium even when the filler is added thereto in an amount sufficient in order to enhance the durability thereof.
To accomplish the aims, in a first aspect of the present invention, there is provided a magnetic recording medium comprising:
a non-magnetic base film; and
a magnetic recording layer comprising a binder resin, magnetic particles, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm,
the said black composite hematite particles comprising:
hematite particles as core particles;
a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.
In a second aspect of the present invention, there is provided a magnetic recording medium comprising:
a non-magnetic base film; and
a magnetic recording layer comprising a binder resin, magnetic particles, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm,
the said black composite hematite particles comprising:
hematite particles as core particles, having a coat formed on at least a part of the surface of hematite particles, which coat comprises at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO2, based on the total weight of the hematite particles;
a coating layer formed on surface of the said hematite particle having the said coat, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.
In a third aspect of the present invention, there is provided a magnetic recording medium comprising:
a non-magnetic base film; and
a magnetic recording layer comprising a binder resin, as magnetic particles magnetic metal particles containing iron as a main component, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm
the said black composite hematite particles comprising:
hematite particles as core particles;
a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.
In a fourth aspect of the present invention, there is provided a magnetic recording medium comprising:
a non-magnetic base film; and
a magnetic recording layer comprising a binder resin, as magnetic particles magnetic metal particles containing iron as a main component, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm
the said black composite hematite particles comprising:
hematite particles as core particles, having a coat formed on at least a part of the surface of the hematite particles, which coat comprises at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO2, based on the total weight of the hematite particles;
a coating layer formed on surface of the said hematite particle having the said coat, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.
In a fifth aspect of the present invention, there is provided a magnetic recording medium comprising:
a non-magnetic base film;
a non-magnetic undercoat layer formed on the non-magnetic base film; and
a magnetic recording layer formed on the non-magnetic undercoat layer, comprising a binder resin, magnetic particles and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm
the said black composite hematite particles comprising:
hematite particles as core particles;
a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.
In a sixth aspect of the present invention, there is provided a magnetic recording medium comprising:
a non-magnetic base film;
a non-magnetic undercoat layer formed on the non-magnetic base film; and
a magnetic recording layer formed on the non-magnetic undercoat layer, comprising a binder resin, magnetic particles, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm
the said black composite hematite particles comprising:
hematite particles as core particles, having a coat formed on at least a part of the surface of the hematite particles, which coat comprises at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO2, based on the total weight of the hematite particles;
a coating layer formed on surface of the said hematite particle having the said coat, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of said hematite particles.
In a seventh aspect of the present invention, there is provided a magnetic recording medium comprising:
a non-magnetic base film;
a non-magnetic undercoat layer formed on the non-magnetic base film; and
a magnetic recording layer formed on the non-magnetic undercoat layer, comprising a binder resin, as magnetic particles magnetic metal particles containing iron as a main component, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm the said black composite hematite particles comprising:
hematite particles as core particles;
a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.
In an eighth aspect of the present invention, there is provided a magnetic recording medium comprising:
a non-magnetic base film;
a non-magnetic undercoat layer formed on the non-magnetic base film; and
a magnetic recording layer formed on the non-magnetic undercoat layer, comprising a binder resin, as magnetic particles magnetic metal particles containing iron as a main component, and as a filler black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm
the said black composite hematite particles comprising:
hematite particles as core particles, having a coat formed on at least a part of the surface of the hematite particles, which coat comprises at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO2, based on the total weight of the hematite particles;
a coating layer formed on surface of the said hematite particle having the said coat, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.
In a ninth aspect of the present invention, there is provided a filler comprising black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm and comprising:
hematite particles as core particles;
a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.
In a tenth aspect of the present invention, there is provided a filler comprising black composite hematite particles having an average diameter of 0.08 to 1.0 xcexcm and comprising:
hematite particles as core particles, having a coat formed on at least a part of the surface of the hematite particles, which coat comprises at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon in an amount of 0.01 to 50% by weight, calculated as Al or SiO2, based on the total weight of the hematite particles;
a coating layer formed on surface of the said hematite particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtained from an alkoxysilane compounds,
(2) polysiloxanes or modified polysiloxanes, and
(3) fluoroalkyl organosilane compounds obtained from a fluoroalkylsilane compounds; and
a carbon black coat formed on the said coating layer comprising at least one organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said hematite particles.